Heat-protective coating



March 2l, 1961 N. F. BAIRD 2,975,556

HEAT-PROTECTIVE COATING Filed Sept. -24, 1957 O '7"O @"2" C) AMPM/9W FTEff/BD.

normally fabricated of brass. creased costs of brass have made iteconomically desir-4 able to substitute aluminum in place oft-the brass.This substitution of aluminum has the disadvantage that the aluminumbase shell has `a tendency to melt somewhat United States PatentHEAT-PROTECTIVE COATING Norman F. Baird, Bloomfield, NJ., assignor toWastinghouse E lectric Corporation, East Pittsburgh, Pa., a corporatlonof Pennsylvania Y y Filed sept. 24, 1957, ser. No. 685,865

6 claims. (cl. 49-7s) This invention relates to heat-protective coatingsand,; more particularly, to heat-protective coatings forl processingaluminum base shells for lamps.

Incandescent lamp bases are prepared .by rst stamp- I ing a base shellinto a predetermined configuration-which 1s normally generallycylindrical and threaded, termi-l nating in an inwardly-projected lip atthe lower extremities of the base shell. trical contact for the lamp. Aneyelet which is fabri-j cated of an electrically-conductive materialsuch as brassis positioned in a centrally-disposed location" adjacentthe lower extremities of the base shell proper, and this eyelet iselectrically insulated from the base shell `by an insulating button suchas glass. This eyelet forms aa second electrical contact for theincandescent lamp;

In the normal procedures of fabricating the lamp base,` the eyelet andbase shell are placed into a mold and'- molten glass is inserted orpoured into the lower inter1or surfaces of the base shell and abouttheeyelet. This electrically insulates the eyelet from the base shell andserves to secure the eyelet in a centrally-disposedI position adjacentthe lower extremities of the base'shell. In the practices of the priorart, the base shells were In `recent years, the in- 2,975,556 PatentedMar. 2 1, 1961 phat'e and sodium polyacrylate a water-vehicle;

1 the constituents of the coating are maintained within'perl descent'lamp incorporating an aluminum base;

This base shell forms one elec-g Fig, 2 isa sectional elevation of anunprocessed alumif num base Shell; v :Fig- 3 isa perspective View of anelectrically-conducting eyelet `before incorporation into the lamp base;

Fig-4 isa diagrammaticplanview of an apparatus for processing lampbases, generally illustrating the opera# tions at various stations;l.lf-iig. 5 is a fragmentary, sectional view taken at station 3 in Figi4 showing the -application of the heat-protec tive coating; j Y

Eig. 6 `is a fragmentary, sectional-view taken at staiV tion 4 in Fig. 4showing the glassing operation; Fig 7 is a fragmentary, sectional viewtakenatstation 6 in Fig. 4 showing the plunger-die operation for form`Tingthe lpoured glass into the desired-conguration.

Althoughthe principles of the invention are generallyi applicable to anytype of lamp which desirably incor porates an aluminum base, theinvention has particular, reference with regard to -bases forincandescent-type lamps" and hence it has been so illustrated .and willbe sol With specilic reference to the form ofthe invention illustratedin the drawing, in iFig. lis shown an incan; descent lamp 10 whichgenerally comprises an envelopej 12, base 14, lead conductors 16hermetically'seale'd through a stem press 18 and `sup-porting anincandes. cible lament 20 between their inwardly-extending extremities.One of the lead conductors is electrically connected to the Ialuminumbase shell 22, which forms;

t one contact electrode for the lamp. The other leadl con-L.

during the so-called glassing operation when the moltenj glass is pouredinto the base shell. The melted aluminum sometimes forms alow-resistance pathebetween the eyelet and the base shell, therebyshorting out the lamp, and the melted aluminum is also objectionablefrom the standpoint of appearance. While the primary purpose of anincandescent lamp is to convert electrical energy into light, theesthetic appearance of-the lamp in the unburned condition is also afactor in promoting its initial sale to the user so that the maintenanceof the base shell in as pleasing an appearance as possible is of greatimportance.

. In order to overcome the foregoing and other diicultiesof andobjections to the prior art, it is the general object of this inventionto provide a heat-protective coating for processing aluminum base shellsin order to prevent any melting of the aluminum base shell.

-It is a further object to provide a method for glassing an aluminumbase shell for a lamp wherein any tendency of` the aluminum to meltduring the glassing operation is substantially inhibited.

It is another object to provide a method for glass` ing an aluminum baseshell for a lamp wherein thinner baseshells may be used.`

The aforesaid objects of the invention, and other 'objects which willbecome apparent as the description proceeds, are achieved by providing aheat-protective coat# ing for processing aluminum base shells, whichcoating principally comprises an adrnixture of sodium borophosshell 22and this coating may be applied as asprayb ductor is electricallyconnected to the centrally-disposedl and electrically-conducting eyelet24, which eyelet isf electrically insulated from aluminum base shell byVax insulating button 26 which may be fabricated of glass; Suchy -a lampconstruction is generally well known.

In Fig. 2 is shown an aluminum base shell 22, beforei the glassingoperation and such a base shell normally" has agenerally-hollow-cylindrical and threaded coniguration. lThe lowerportion of the base. shell formsv 'anl inwardly-projecting lip 28 whichserves to hold'the glass insulating button 26.

In Fig. 3 is shown the electrically-conductingeyelety 24 which may bepunched from brass, Ifor example, and? which eyelet has acentrally-disposed aperture 30 form ing a retaining lip which cooperateswith thel pouredglass insulating button 26 to retain the eyeletin posifltion. "f j In Fig. 4 is shown a diagrammatic plan view of a base-.fabricating machine 32, modiied slightly to provide f olf4 theapplication of the heat-protective coating as described herein. Suchmachines arel normally designedl to .be indexed through a plurality ofpositions orwork station; and at the station designated 1, the yeyeletZ4 is fedi' into the-receiving mold by conventional techniques. thestation designated 2,l thebase shell 22 isfed f, the receiving mold byconventional practices. Atythfe; station designated 3 theheat-protective ,eoatinggis-apw plied to at least the :lower interior'portionsoffithebse the' Baseshell z2.l 'This' moltenrglass `serves toseparate the eyelet z4gfr'o`m A'the base shell 22. Thereafter, excessivefglass -is blown from the upper surfaces of the molds and from betweenthee-'molds at the glass-cutter stations designated '5 4and this alsoserves to partially cool the pouredf'glia's's. At the station designated6, a glass plunger for swt-he interior surfaces of the poured glass intoa generally conical configuration `so that when the center lamp"l'ea'dwire is later inserted into 'the base, it will be directed towardthe aperture 30 in the centrally- 'dispose'd e'y'let 24. At the stationdesignated 7,? an auxiliary glass plunger `serves 'further to cool thepoured glass in order to secure Jthe eyelet 24 in the cooled glassbutton 26 and to secure the `cooled glass button 26 lin the base shell22. vAt the station designated 8, a pin plunger removes any residue ofglass from the aperture 30 -of the centrally-disposed eyelet Z4 andthereafter at shel 22h51 means ofa conventional atornizerv 36. If

desired, the'heaft-pro'tective coating could be applied to the, baseshell 22 before the base shell was placed on the coatingV machine, butit is far more convenient automagically to apply this coa-fing after theshell 22 has' The heat-protective coating principally comprises 'from31o-30% by weight sodium'borophosphate, from 10% to 15% by weightVsodium polyacrylate'and from n55% to 87% by Weight/Water. l The moltenglass which Vis poured into the base shell during the glassing operationmay have Ala temperature of from 1`l8`5 C. to l200 C., for example and,as noted hereinbefore, the aluminum uuderthese conditions has a markedtendencyto melt, at` least in discrete portions.V The heat-protectivecoating, as Yhereinbefores'peciiied, forms a barrier or heatprotectivelayer` between 'the molten vglass andthe aluminuxn base shell',substantially inhibiting any tendency for the' aluminumfba'se shell tomelt.

Kegalfdingthe constituents of the heat-protective coating, sodiuml borophospha'tehasv a high Water of hydrationand also has the property ofencasing steam at'highV temperatures. Theencasedsteam serves they dualVfunction'of providing an excellent insulating layer and also im'p'airingthe v'adhe`renc'e of the sodium borophosphate for ,the'base' shell,which isf/highly vdesirable `as will be explained hereinafter. Asolution of sodium bo'rophosphate in Water, however, has a relativelylow viscosity and will not `adhere `to the aluminum base shell insufficient amounts ,to provide the proper degree of protection duringthe glassing operation- Sodium poly'acirylate vhas ya high, viscosity,is yreadily soluble inwalter, as is'sodium borophosphate, and sodiumpolya't:ryl'atev has ahigh heatof vaporizationl This material, however,tendsjto leave a 'carbonacleou's residue after beingheated, whichresidueisrn'ot readily removed hva water wash; rlffhis residue impairs theappearance of the vcompleted base 'and alsotends to formlow-electrical-resistanee pat-hs;

When f'amixtuie fof sodium' borophosphate and sodium polyacrylate 1in'water solution is utilized as a heat-protective coating, the benets ofboth of these constituents are realized. Thus the` admixtu-re'hasVsuflicent viscosity (for Vexample 32 c.p.s.) to provide an adequateamount of the heat-protective coating on the base and the steam which isencased by the sodium borophosphate renders the admixture very poorlyadherent to the aluminum base shell at high temperatures. Thus anycoating residue is readily -removed by a water Wash. In addition, thein- I dividual constituents of lthe admixture both -have a very ance ofthe heat-protective coating. A

If less than the indicated proportionscomprising the admixture are used,the beneicial effects ofY the heatprotective coating are minimized. Iftheproportions of the sodium borophosphate land the polyacrylate aregreater than the maximum permissible amounts indicated hereinbefore, theviscosity of the resulting coating tends to be excessive and anexcessive amount of thecoatng material isdepsited. In addition, there issometendency for residues where a Vrelatively -l'ar'ge amount tof'coating material has to be reinoved by ag'wa'ter wash andthe adherenceof the coating material for the aluminum vbase shell is somewhatincreased, which also inhibits the re-l moval of the vcoating' materialby ali/'atei- Wash, v The preferred formulation for ythe heat-protetivevcoating is about 5% byweight sodium borophosphate,-about 10% by weightsodium polyarylate and about y% by weight water. l Y g x I t is alsopossible to incorporate s mall anouiitsof otherY additives into theheat-protective 4coating Yand Yif desired, 5% by Weight of ammoniumpolyacrylte may be 'sbs'tituted'inplace of an equivalent -ainontofl ivehicle in th'egfor'e'goin'g preferred specific embodiment. Thissomewhat increases the capacity for-heat absorption of the coat-ing',but such other smallv additives are notl necessary fo'r good results.Other materialsmay be substituted in place 'ofthe ammonium polyarylatevadditive, *such Vas an equivalent weight of potassium silicate,for-example. v i j I In Fig. 6 is shown they glassing operation at thestation designated"4 in Fig'. 4'. In this operation, a pree determinedamount of molten glass is poured or inserted into'the coated base, suchglassipou'ring techniques being Well known.y As a specific eiiample, inthe case 'of `a medium-'screw type base,"about 3.6 grains ofl glass maybe lused'.` The glass may vary,'but 'as a vspeciiic example, it mayhave' thecoinpos'it'ion of 9.5% by weight cullet glass', '2.52% byVweight MnOZ, 1.26% by weight KNO3, 0.87% by weightlNHg) 2SC., and `0.35%by weight Cr203. The cullet glass, as'V "usedV herein, has thecomposition 76.8%- by weight Si02, 17.4% lb'y Weight NaZO, 0,6% byweight K2`O, `0;4% byweight CaO' and 316% by weight Mg'O. It should beunderstoodV th'at this glass is only given vby way of specic example andother glasses and glassing lcomposi'tions' may be substituted. V

, In Fig'. 7 is shown the glass-forming'operation at the stationdesignated"6 in Fig. 4. In this operation the glass-forming plunger 38provides the interior surface of thepouredglass with an inverted,generally-conical configuration inforider that thecenter lead wire maybeinserted, 'into the eyelet by automatic equipment.V The plungerstation follows the glass pouring station ata sufficient time `intervalthat the glass has 'partiallyyco'oled so that it isin aaplasticistat'erather than la molten state. Thereafter,-at the staion designated ".7 inFig. V4,J a` conventional auxiliaryglass plunger whichV is internallycooled with water, for `example, isV inserted into the base in ordertosubstantiallycool the poured glass. An additional plunger, 'not shown,punches any residual Vglass which may'remain'within thecentrally-disposed aperture 30 within the eyelet 24 inorder that thecenter'lead wire may be inserted therethrough during'theplampfabricadirt and other impurities as well as the residual heatprotectivecoating which remains.

In the cleaning process, any commercial cleaner may be used and thebases are placed into the cleaningy solutions and agitated. This removessubstantially all traces of dirt and other impurities as well asresidual heat-protective coating. By way of specic examples of suitablecleaning solutions, the bases may be agitated in a dilute solution ofnitric and sulphuric acid at a concentration of 40 to 45 Baume.Alternatively, the bases may be cleaned with a 5% solution of ammonicalsoap or with a 3% to 5% lauryl-sulphate-type detergent, such as iscommercially available under various trademarks. Othercommercially-available cleaning solutions may be substituted for thespecific examples given hereinbefore.

It may be desirable in some cases to dispense with the eyelet and tosecure the lead wire to the exterior surface of the glass insulatingbutton 26 by means of an epoxy-resin cement, for example. In such anembodiment, the procedures used in fabricating the base would beidentical with those as outlined hereinbefore, except that the eyeletwould not be placed into the mold.

The foregoing steps need not be carried out on the automatic equipmentas outlined hereinbefore, but may be carried out by hand, if desired,although from the production standpoint, it is economically desirable tofabricate the bases on an automatic basis.

A further advantage of the heat-protective coating disclosed herein isthat the aluminum base shells may be made thinner, if desired, thuseliminating the cost of using added aluminum in the base shells. tion,in the practices of the prior art it has been necessary to provide thealuminum base shell with a certain minimum thickness, for example .0125inch for a mediumscrew-type base, in order that the aluminum base shellhas suiiicient thermal capacity to absorb suflicient heat from themolten glass to prevent excessive melting of the aluminum. Even withthis thickness of the aluminum base shell, considerable melting of thealuminum has been encountered. Where the heat-protective coating isinterposed between the molten glass and the aluminum base shell, thethermal capacity required for the aluminum base shell is decreased and amedium-screW-type base shell having a thickness of only .0105 inch isgenerally satisfactory and will display substantially no meltedportions.

It will be recognized that the objects of the invention have beenachieved by providing a heat-protective coating for processing aluminumbase shells as well as a method for processing aluminum base shellswherein any melting of the aluminum due to the molten glass issubstantially eliminated. In addition, the aluminum base shells may bemade thinner, if desired.

While in accordance with the patent statutes, one bestknown embodimentof the invention has been illustrated and described in detail, it is tobe particularly understood that the invention is not limited thereto orthereby.

I claim:

l. A heat-protective'coating for processing aluminum base shells forlamps, said coating principally comprising from 3% to 30% by weightsodium borophosphate, from to 15% by weight sodium polyacrylate, andfrom 55% to 87% by weight Water.

2. A heat-protective coating for processing aluminum base shells forlamps, said coating principally comprising about 5% by weight sodiumborophosphate, about 10% by Weight sodium polyacrylate, and about 85% byweight Water.

3. The method of glassing an aluminum base shell for a lamp, comprisingapplying to at least the lower interior surfaces of the aluminum baseshell a heat-protective `coating principally comprising from 3% to 30%by weight sodium borophosphate, from 10% to 15% by In explanaweightsodium polyacrylate and from 55% to 87% by Weight water, inserting apredetermined amount of molten glass into a mold containing said coatedbase shell to till a selected portion of said coated base shell, coolingsaid base and said glass to secure said glass in said base, andthereafter cleaning said base with a cleaning solution to removeresidual heat-protective coating.

4. The method of glassing an aluminum base shell for a lamp, comprisingapplying to at least the lower interior surfaces of the aluminum baseshell a heat-protective coating principally comprising about 5% byWeight sodium borophosphate, about 10% by weight sodium polyacrylate andabout by Weight water, inserting a predetermined amount of molten glassinto a mold containing said coated base shell to fill a selected portionoi coated base shell, cooling said base and said glass to secure saidglass in said base, and thereafter cleaning said base with aWater-vehicle cleaning solution to remove residual heat-protectivecoating.

5. The method of forming in an aluminum base shell for a lamp a glassinsulating section having embedded therein a `centrallydisposed andelectrically-conducting eyelet insulated from said base shell,comprising placing said eyelet and said base shell into a mold andapplying to at least the lower interior surfaces of said base shell aheat-protective coating principally comprising from 3% to 30% by weightsodium borophosphate, from 10% to 15% by Weight sodium polyacrylate `andfrom 55% to 87% by weight water, inserting into said incid apredetermined amount of molten glass covering said eyelet and the lowerinterior surfaces of said base shell and separating said eyelet fromsaid base shell, partially cooling said glass, forming the uppersurfaces of said partially cooled glass into a predeterminedconfiguration, further cooling said formed glass to secure said eyeletin said cooled glass and to secure said cooled glass in said base shell,and thereafter cleaning said base with water-vehicle cleaning solutionto remove residual heatprotective coating.

6. The method of forming in an aluminum base shell for a lamp a glassinsulating section having embedded therein a centrally-disposed andelectrically-conducting eyelet insulated from said base shell,comprising placing `said eyelet and said base shell into a mold andapplying to at least the lower interior surfaces of said base shell aheat-protective coating principally comprising about 5% by weight sodiumborophosphate, about 10% by Weight sodium polyacrylate and about 85% byWeight water, inserting into said mold a predetermined amount of moltenglass covering said eyelet and the lower interior surfaces of said baseshell and separating said eyelet from said base shell, partially coolingsaid glass, forming the upper surfaces of said partially cooled glassinto a predetermined configuration, further cooling said formed glass tosecure said eyelet in said cooled glass and to secure said cooled glassin said base shell, and thereafter cleaning said base with awater-vehicle cleaning solution to remove residual heat-protectivecoating.

References Cited in the file of this patent UNITED STATES PATENTS1,011,586 Criggal Dec. 12, 1911 1,976,679 Fikenstscher et al. Oct. 9,1934 2,158,044- Haller May 9, 1939 2,387,865 Kleeck Oct. 30, 19452,413,146 Larson Dec. 24, 1946 2,439,395 Leatherman Apr. 13, 19482,480,790 Truhlar Aug. 30, 1949 2,538,589 Poje Ian. 16, 1951 FOREIGNPATENTS 797,345 France Feb. 8, 1936

1. A HEAT-PROTECTIVE COATING FOR PROCESSING ALUMINUM BASE SHELLS FORLAMPS, SAID COATING PRINCIPALLY COMPRISING FROM 3% TO 30% BY WEIGHTSODIUM BOROPHOSPHATE, FROM 10% TO 15% BY WEIGHT SODIUM POLYACRYLATE, ANDFROM 55% TO 87% BY WEIGHT WATER.
 3. THE METHOD OF GLASSING AN ALUMINUMBASE SHELL FOR A LAMP, COMPRISING APPLYING TO AT LEAST THE LOWERINTERIOR SURFACES OF THE ALUMINUM BASE SHELL A HEAT-PROTECTIVE COATINGPRINCIPAL COMPRISING FROM 3% TO 30% BY WEIGHT SODIUM BOROPHOSPHATE, FROM10% TO 15% BY WEIGHT SODIUM POLYACRYLATE AND FROM 55% TO 87% BY WEIGHTWATER, INSERTING A PREDERTEMINED AMOUNT OF MOLTEN GLAS INTO A MOLDCONTAINING SAID COATED BASE SHELL TO FILL A SELECTED PORTION OF SAIDCOATED BASE SHELL, COOLING SAID BASE AND SAID GLASS TO SECURE SAID GLASSIN SAID BASE, AND THEREAFTER CLEANING SAID BASE WITH A CLEANING SOLUTIONTO REMOVE RESIDUAL HEAT-PROTECTIVE COATING.